1. Field of the Invention
The present invention relates to a full-color light source unit. Particularly, it relates to a full-color light source unit that can exhibit various color tones efficiently freely. Moreover, it relates to an improvement of a unit to be suitably used also as a white light source for back-lighting or front-lighting of a full-color liquid-crystal panel.
The present application is based on Japanese Patent Applications Nos. Hei. 11-320425 and 2000-140772, which are incorporated herein by reference.
2. Description of the Related Art
Use of LEDs emitting three primary colors (RGB) of light as a full-color light source is known generally. In such a general full-color light source, one red LED, one green LED and one blue LED were packed in one package. Such a full-color light source can emit desired-color light as well as white light under suitable control on the respective LEDs.
For example, a surface light source disclosed in JP-A-10-319396 is used as a white light source for a liquid-crystal panel. In the surface light source, a blue LED is used as a light source. The blue LED is arranged in an end portion of a first rod-like light guide plate. The first light guide plate is attached to a light entrance surface of a second panel-like light guide plate. A layer of a color conversion member made of a fluorescent material is formed in a portion of the first light guide plate opposite to the light entrance surface of the second light guide plate. The color conversion member absorbs blue light emitted from the blue LED and emits yellow light. As a result, the yellow light emitted from the color conversion member and the blue light emitted from the blue LED are mixed together to synthesize white light. The white light is made incident into the second panel-like light guide plate. Thus, the second light guide plate serves as a white surface light source for back-lighting of a liquid-crystal panel.
The white light emitted from the white surface light source disclosed in JP-A-10-319396 is, however, a mixture of the blue light emitted from the blue LED and the yellow light emitted from the fluorescent material. Hence, it is difficult to develop red when full-color display is to be achieved by liquid crystal. This is because the white light contains a slight amount of red light component. Moreover, there is a problem in the durability of the fluorescent material because the fluorescent material is apt to change with the passage of time compared with LED. Moreover, 100% of the light emitted from the blue LED does not appear on a light-emitting surface and a conversion loss occurs in the conversion of the blue light into the yellow light because the blue light emitted from the blue LED is mixed with the yellow light due to the conversion of a part of the blue light. Hence, there is also a problem that sufficient light-emitting efficiency cannot be obtained. In addition, the tone of color cannot be changed.
According to a general full-color light source using LEDs with three primary colors (RGB) of light, full-color light containing a sufficient amount of red light component can be generated. If white light developed by such a full-color light source is used for back-lighting of a full-color liquid-crystal panel, red can be expressed sufficiently even in the full-color liquid-crystal panel. Therefore, the inventors of the present invention have made investigation and investigation into a full-color light source using RGB LEDs efficiently and the use of the full-color light source for lighting of a full-color liquid-crystal panel. As a result, the inventors have found the following problem.
In characteristic of currently generally available LEDs, a green or red LED is inferior in the light emission output (Luminance) to a blue LED. For example, in a full-color light source unit having one blue LED, one green LED and one red LED, therefore, it was necessary to suppress the output of the blue LED to balance with the outputs of the green and red LEDs.
Such balance, however, makes efficiency worse because the blue LED cannot emit light with full power. Particularly in a white surface light source to be used in a portable apparatus, such balance is undesirable because high efficiency is required from the point of view of power consumption saving.
Further, another problem which the inventors have found will be described.
JP-A-11-329044 discloses a background-art light-emitting system for back-lighting of a full-color liquid-crystal panel.
The light-emitting system comprises a row of LED chips, and a light guide portion for receiving light from the row of LED chips through an incident surface of the light guide portion and making the light propagate through the inside of the light guide portion to thereby make surface-like back-lighting beams exit from an exit surface of the light guide portion. The row of LED chips are constituted by red (R), green (G) and blue (B) LEDs. Each of the R, G and B LEDs has a narrow-band emission spectrum. Hence, when the R, G and B LEDs are made to emit light, R, G and B light components emitted from the LEDs are mixed to get her so that the liquid-crystal panel can be irradiated with white back-lighting beams.
According to the background-art light-emitting system using light-emitting devices with three colors R, G and B, however, the number of wire-bonding points became so large that the light-emitting devices could not be mounted compactly because each of the G and B light-emitting devices had positive and negative electrodes on the light-emitting surface side. Hence, the distance between adjacent ones of the light-emitting devices became so large that it was difficult to achieve a point light source. Moreover, improvement in color balance was limited. Moreover, when the light-emitting devices were increased in number, the total heating value became so large that the output power is lowered, the life of the light-emitting system is shortened, etc.
An object of the present invention is to provide a full-color light source unit that can exhibit various color tones efficiently freely.
Another object of the present invention is to provide a light-emitting system in which reduction in size can be made in the case of use of a plurality of light-emitting devices to thereby make improvement in color balance possible.
Still another object of the present invention is to provide a light-emitting device in which lowering of output power and shortening of the life of the light-emitting system can be avoided in the case of use of a plurality of light-emitting devices.
In order to achieve the above objects, according to an aspect of the present invention, there is provided a light-emitting system comprising a plurality of light-emitting devices mounted on a substrate, wherein: the plurality of light-emitting devices include a first group of light-emitting devices and a second group of light-emitting devices, each of the first group of light-emitting devices having first and second electrodes on a light-emitting surface side, each of the second group of light-emitting devices having a first electrode on the light-emitting surface side and a second electrode on a side opposite to the light-emitting surface side; and the first group of light-emitting devices and the second group of light-emitting devices are arranged alternately in a line on the substrate.
According to the aforementioned configuration in which the first group of light-emitting devices each having two electrodes on the light-emitting surface side and the second group of light-emitting devices each having one electrode on the light-emitting surface side and one electrode on the substrate side are arranged alternately on the substrate, the light-emitting devices can be mounted compactly because the light-emitting devices can be connected easily by bonding wires even in the case where the light-emitting devices are arranged densely. Incidentally, the concept xe2x80x9csubstratexe2x80x9d used herein includes a printed-circuit board in which leads to be connected to the first and second electrodes are printed on the board by a circuit-printing technique, a lead frame-structural substrate formed by a technique in which an electrically insulating material is injected into a mold in the condition that a lead frame corresponding to the leads to be connected to the first and second electrodes is arranged in the mold, etc. The concept xe2x80x9clight-emitting devicexe2x80x9d means a bare chip such as an LED provided with first and second electrodes.
According to another aspect of the present invention, there is provided a light-emitting system comprising a plurality of light-emitting devices mounted on a substrate, wherein: the substrate includes a common lead being common to the light-emitting devices, and individual leads being peculiar to the light-emitting devices respectively, the common and individual leads being formed as predetermined patterns on a front surface of an electrically insulating base; and each of the common lead and the individual leads has a portion extended to one side surface of the electrically insulating base.
According to the aforementioned configuration, the heat-radiating area of the light-emitting system increases as a whole because each of the leads to be connected to the light-emitting devices is extended from a front surface of the substrate to a side surface of the substrate.
According to a further aspect of the present invention, there is provided a light-emitting system comprising a plurality of light-emitting devices mounted on a substrate, wherein: the light-emitting devices include a first group of light-emitting devices capable of emitting light with a predetermined heating value, and a second group of light-emitting devices capable of emitting light with a heating value smaller than the predetermined heating value; and the first group of light-emitting devices and the second group of light-emitting devices are arranged in a line on the substrate so that the first group of light-emitting devices are not adjacent to one another.
According to the aforementioned configuration, heat generated by the plurality of light-emitting devices can be dispersed.
According to a still further aspect of the present invention, there is provided a light-emitting system comprising a plurality of light-emitting devices mounted on a substrate, wherein: the light-emitting devices include a first group of light-emitting devices with a predetermined height, and a second group of light-emitting devices with a height lower than the predetermined height; and the first group of light-emitting devices and the second group of light-emitting devices are arranged in a line on the substrate so that the first group of light-emitting devices are not adjacent to one another.
According to the aforementioned configuration, light radiation from one member in the first group of light-emitting devices to the outside can be prevented from being disturbed by other members in the first group of light-emitting devices.
The present invention has been attained to solve the problem and the configuration thereof is as follows.
That is, a full-color light source unit comprises: at least one blue LED; green LEDs larger in number than the blue LED; and red LEDs larger in number than the blue LED.
According to the full-color light source unit configured as described above, green LEDs and red LEDs low in light emission output are set to be larger in number than the blue LED high in light emission output. Hence, white light can be generated while the outputs of the respective LEDs are balanced with one another without any limitation on the output of the blue LED. Hence, there is no lowering of efficiency in light emission.
The respective numbers of blue, green and red LEDs are not particularly limited. In consideration of the demand for miniaturization on the liquid-crystal panel, it is preferable that the full-color light source unit comprises one blue LED, two green LEDs, and two red LEDs. According to the inventors÷ investigation, it has been found that optimum white light is obtained in the aforementioned combination of currently available LED when the respective LEDs are made to emit light with nearly full power.
It is preferable that the green LEDs are made equal in number to the red LEDs.
It is preferable that a bare chip type LED is used as each of the LEDs and that all the LEDs are packed in a package (housing).
From the necessity for bonding work, or the like, a predetermined distance is taken between adjacent ones of the LEDs in the full-color light source unit. Hence, the full-color light source unit cannot emit white light directly. White light can be only obtained when light components emitted from the respective LEDs in the full-color light source unit are mixed together in a light mixing portion. It has been realized that the arrangement of the respective LEDs must be considered in this occasion so that the light components emitted from the respective LEDs can be mixed efficiently in the light mixing portion or in other words the light components can be mixed sufficiently even in a small-size light mixing portion.
It is first necessary that the blue LED smallest in number and highest in single output is placed in the center of the arrangement of LEDs. The xe2x80x9carrangement of LEDsxe2x80x9d includes so-called linear arrangement in which LEDs are arranged in a line, so-called planar arrangement in which LEDs are arranged radially or two-dimensionally to cover all over a plane, and so-called volumetric arrangement in which LEDs are arranged three-dimensionally. Incidentally, in consideration of the fact that a light entrance surface of a surface light source to be used for back-lighting or front-lighting of a liquid-crystal panel is shaped like a narrow plane, it is preferable that LEDs are arranged in a line in accordance with the shape of the light entrance surface.
In the arrangement of LEDs, it is preferable that green LEDs and red LEDs are arranged symmetrically with respect to the blue LED disposed as the center of the arrangement. That is, when B, G and R express a blue LED, a green LED and a red LED respectively, the following arrangement patterns are used preferably.
(Arrangement Pattern 1) G-R-B-R-G
(Arrangement Pattern 2) R-G-B-G-R
Of these, the arrangement pattern 1 is especially preferred. Both positive and negative electrodes are provided on the upper surface of each of general blue and green LEDs whereas only one electrode is provided on the upper surface of each of general red LEDs. This is because in consideration of wire-bonding workability and proximate arrangement of LEDs with avoiding crossing of wires, it is preferable that red LEDs small in the number of electrodes are arranged on the side as near to the center as possible.
From the point of view of facilitation of wire-bonding work, or the like, the following LED arrangement pattern may be used.
(Arrangement Pattern 3) R-R-B-G-G
Besides the aforementioned LED bare chips, a wiring portion for wiring the LEDs, a transparent resin for enclosing the LEDs, a housing, etc. are provided in the full-color light source unit. Bonding pads are provided in the wiring portion. The bonding pads are wire-bonded to the electrodes of the LEDs respectively. The wiring portion further has a connector, by which the respective LEDs are electrically connected to external power supply lines and control lines.
The full-color light source unit is combined with a light mixing portion to constitute a full-color light source.
That is, light components emitted from the respective LEDs of the full-color light source unit are mixed together in the light mixing portion to thereby generate various kinds of light. The light mixing portion is made of a light-transmissible material (such as methacrylic resin, polycarbonate, or the like). The light mixing portion has a light entrance surface in which light components emitted from the respective LEDs are incident, a mixing means for mixing the incident light components, and a light-emitting surface for emitting the mixed light. The light mixing portion may be made of lens-like glass or resin with which the respective LEDs are merely covered and which condenses and mixes light. Alternatively, the light mixing portion may be made of glass or resin containing a light scattering material.
Further, the light mixing means may be constituted by a portion 115 having a light scattering material and/or a portion 111 having a light reflection surface 113 as described in the tenth embodiment (see FIGS. 16A to 16C) of the present invention. The light reflection surface is obtained by surface roughening such as etching, sandblasting, electric discharging, or the like, or by white-printing or by white tape-sticking.
A surface light source is constituted by a combination of the full-color light source and a surface light guide portion.
The surface light guide portion is made of a light-transmissible material (such as methacrylic resin, polycarbonate, or the like). The surface light guide portion is shaped like a plate corresponding to a liquid-crystal panel. The surface light guide portion has a light entrance surface and a light-emitting surface through which light is transmitted. Other surfaces of the surface light guide portion than these surfaces are preferably provided as reflection surfaces. The reflection surfaces are formed by surface roughening such as etching, sandblasting, electric discharging, or the like, or by white-printing or by white tape-sticking. There is also an effect that light components emitted from the respective LEDs and transmitted through the light mixing portion are further mixed through the reflection surfaces. Preferably, the reflectivity of the reflection surfaces is set to increase as the location in the reflection surfaces becomes farther from the light entrance surface. That is, it is preferable that light is emitted uniformly from the light-emitting surface. Moreover, preferably, gradient may be given to the thickness of the surface light guide portion (the thickness of the light entrance surface side may be thickened) as described in the eight embodiment (see FIGS. 14A to 14C) of the present invention so that light made incident into the surface light guide portion from the light entrance surface is reflected efficiently toward the light-emitting surface.
Features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.